Hydraulically powered diaphragm pump with pretensioned diaphragm

ABSTRACT

In a hydraulically driven diaphragm pump with a diaphragm clamped at its edge between a pump body ( 2 ) and a pump cover ( 3 ), separating a delivery chamber ( 4 ) from a hydraulic chamber ( 5 ) and pretensioned in the direction of its suction stroke by spring force, and with a hydraulic diaphragm drive in the form of an oscillating displacement piston ( 6 ) which is displaceable in the pump body ( 2 ) between a reservoir chamber ( 8 ) for the hydraulic fluid and the hydraulic chamber ( 5 ), characterised in that the diaphragm ( 1 ) is so strongly pretensioned by means of spring force that it exerts a substantial compressive force on the hydraulic fluid in the hydraulic chamber ( 5 ) and that therefore a substantial overpressure is built up in the hydraulic chamber ( 5 ) against the delivery chamber ( 4 ).

[0001] Description

[0002] The invention concerns a hydraulically powered diaphragm pumpaccording to the precharacterising portion of claim 1.

[0003] In known diaphragm pumps of this generic type (DE-AS 1 034 030,DE-OS 25 26 925), the diaphragm is pretensioned with a compressionspring. The compression spring is arranged either in the deliverychamber of the diaphragm pump or in its hydraulic chamber, and in such amanner that is assists the movement of the diaphragm in the direction ofthe suction stroke.

[0004] Since it is only a weak compression spring that is concernedhere, it is also only a relatively light pretensioning of the diaphragmthat is provided. This has the result that the diaphragm positionalcontrol is still not satisfactorily provided in every situation.Therefore, additional design elements are necessary for diaphragmpositional control, which naturally complicate the structure of thediaphragm pump and thus make it more expensive.

[0005] In addition to this there is the fact that due to the slightpretensioning exercised by the relatively weak spring, gas formation inthe hydraulic chamber is not effectively prevented during the suctionstroke. Thus, because of the still present gas formation in thehydraulic chamber, the overall suction performance of the knowndiaphragm pumps is limited.

[0006] In diaphragm pumps of this generic type, their start-upreliability is of great significance. In modern diaphragm pumps, thelack of start-up reliability can be regarded as a distinct disadvantage.This is only rectified if additional design devices are present,although these bring additional costs. It is therefore desirable withsuch diaphragm pumps to have sufficient start-up reliability so as toensure that—due to continuous internal leakage—when the pump is at astandstill, the diaphragm will still not move in the direction of thecompression stroke even when there is a vacuum in the delivery chamber.

[0007] The invention is thus based on the aim of so designing thediaphragm pump of this generic type in order to rectify theaforementioned disadvantages that with a simple design, it stillpossesses a high level of dosing accuracy and that its suction power isnot limited by gas formation in the hydraulic chamber so that startingup even from a vacuum is easily possible.

[0008] The features of the invention designed to fulfil this aim arecontained in claim 1. Advantageous further embodiments of this aredescribed in the further claims.

[0009] The diaphragm pump designed according to the invention is basedon the essential concept of pretensioning the diaphragm with springforce so strongly that it exercises a considerable compression force onthe hydraulic fluid in the hydraulic chamber and that therefore asubstantial overpressure is built up in the hydraulic chamber againstthe delivery chamber.

[0010] Advantageously, the spring force is so dimensioned that thediaphragm follows the piston during the suction stroke even if there isa vacuum in the delivery chamber.

[0011] The diaphragm pump designed according to the invention alsoprovides the desired start-up reliability. This is due to the fact thataccording to the invention, the spring force is so dimensioned that whenthe pump is at a standstill the diaphragm does not move in the directionof the compression stroke even if there is a vacuum in the deliverychamber.

[0012] According to a preferred embodiment of the invention, the springforce is so dimensioned that the pressure in the hydraulic chamber isalways at least 1 bar greater than the pressure in the delivery chamber.

[0013] In particular, the design may be carried out in such a mannerthat the spring force is so dimensioned that a differential pressure ofat least 1 bar is always applied to the diaphragm.

[0014] Particular advantages may be achieved with the invention if thespring force is so dimensioned that at no time during the suction strokeis there a negative pressure in the hydraulic chamber, until thediaphragm is mechanically supported on the pump body.

[0015] In a further development of the invention, the design may be soexecuted that the sum total of the differential pressure generated onthe diaphragm by the spring force and the holding pressure of a sprungleakage compensating valve is always at least one bar. It isadvantageous if the differential pressure on the diaphragm is very largecompared with the holding pressure of the leakage compensating valve.

[0016] The dimensioning may, for instance, suitably be so achieved thatthe differential pressure on the diaphragm is dimensioned to be at least0.8 bar and the holding pressure of the leakage compensating valve isdimensioned at about 0.3 bar.

[0017] In this amended embodiment of the invention, it is thereforeadvantageously possible to ensure the suction power of the pump—alsofrom a vacuum—not only through the differential pressure on thediaphragm, but through the total of the differential pressure on thediaphragm and the holding pressure of the leakage compensating valve.

[0018] Provided the aforementioned total is greater than one bar, evenin the presence of a vacuum, uncontrolled breathing should not takeplace. This ensures that the diaphragm follows the piston during thesuction stroke, even under vacuum conditions.

[0019] If the differential pressure on the diaphragm is dimensioned, forinstance, to 0.8 bar at the rear dead point of the diaphragm, a holdingpressure of only 0.3 bar is necessary at the leakage compensating valvein order to achieve the total desired differential pressure of more than1 bar.

[0020] During the leakage compensation process, a negative pressure of0.3 bar arises in the hydraulic oil. Experience has shown that such lowholding pressures at the leakage compensating valve produce nodisadvantage in practice. In corresponding manner, during the suctionstroke and under vacuum conditions, a negative pressure of 0.2 bararises in the hydraulic oil on the suction side given a differentialpressure of 0.8 bar on the diaphragm.

[0021] Such low negative pressures bring with them no disadvantages inpractice. Experience shows that the—unwanted—gas formation in hydraulicoils only occurs to a great extent at larger negative pressures, fromabout 0.4 bar.

[0022] Overall, this produces the advantage that due to the weakerspring loading that is possible, space and costs can be saved.

[0023] From the standpoint of the design, the invention may beadvantageously realised in various ways and through various means. It ispossible, for instance, to generate the strong spring forcepretensioning the diaphragm in the direction of the suction stroke withthe diaphragm itself, i.e. through its shape and/or material. In thisregard, polytetrafluoroethylene (PTFE) comes into consideration as amaterial for the diaphragm, while a suitable diaphragm shape is given,for instance, by suitable preforming.

[0024] In a variant design embodiment, it is also possible according tothe invention to generate the strong spring force pretensioning thediaphragm in the direction of the suction stroke with at least onespring element built into the diaphragm, for instance, a disk spring.

[0025] From the design standpoint, a particularly simple realisation ofthe idea upon which the invention is based is provided if the strongspring force pretensioning the diaphragm in the direction of the suctionstroke is generated by a compression spring arranged in the hydraulicchamber; this may be supported on a central guide rod connected to thediaphragm, on the pump housing at one end, and on the end of the guiderod at the other end, whereby its strength is dimensioned according tothe effective diaphragm area.

[0026] It lies within the scope of the invention that the diaphragm isdesigned as a moulded diaphragm to adapt it to the differential pressureacting upon it. A particularly advantageous design results if themoulded diaphragm has a peripheral bead whose concave side faces towardsthe hydraulic chamber. As a result of the differential pressure actingupon the diaphragm, the bead of the moulded diaphragm is stabilised byit. There is no resultant tendency towards bulging, so that thediaphragm has a long life expectancy. In addition, the tendency tofrictional wear with sandwich diaphragms is extremely low.

[0027] In a further embodiment of the invention, the diaphragm may bedesigned as a sandwich diaphragm with at least two diaphragm layerswhose individual layers are mechanically coupled and, during the suctionstroke, are pulled back by the spring action of the compression springas a complete diaphragm packet.

[0028] It is also within the scope of the invention to realise thedesign such that the diaphragm is supported in its rear dead pointposition by an almost gap-free surface formed by part of the pump bodyand a diaphragm coupling disk.

[0029] Overall, therefore, the invention entails substantial advantages,which may be set out as follows, purely by way of example:

[0030] The suction power of the pump is not limited by unwanted gasformation in the hydraulic chamber, so that suction even from a vacuumis very readily possible. Thus the suction power of the diaphragm pumpaccording to the invention corresponds to that of a piston pump.

[0031] The diaphragm pump according to the invention has a high dosingaccuracy, since gas formation is entirely prevented by the negativepressure according to the invention which prevails in the hydraulicchamber.

[0032] Due to the design of the hydraulic pump according to theinvention, it may be provided with a single simple leakage compensatingvalve, which has only a weak spring or no spring at all, so that duringthe leakage compensation process, hardly any gas formation takes place.

[0033] Due to the strongly reduced or completely prevented gasformation, greatly simplified gas removal from the hydraulic chamberresults, so that no continuous gas removal is required.

[0034] The diaphragm pump according to the invention has a simplestructure overall, so that no additional elements are required fordiaphragm positional control.

[0035] The rotary rate of the pump drive is not limited by gas formationin the hydraulic chamber, so that high rotary rates are possible.

[0036] Due to the overpressure prevailing in the hydraulic chamber, thediaphragm is prevented from moving forward in the direction of thecompression stroke when the pump is stationary, even if there is avacuum in the delivery chamber.

[0037] Due to the overpressure in the hydraulic chamber, the diaphragmis always curved in the direction of the delivery chamber, i.e.preshaped, so that its shape is stabilised.

[0038] The invention will now be described in greater detail withreference to the drawings. These show:

[0039]FIG. 1 a schematic representation of the diaphragm pump accordingto the invention in longitudinal section;

[0040]FIG. 2 a diagram of the differential pressure on the diaphragmover its stroke travel generated purely by the spring force;

[0041]FIG. 3 a diagram of the pressure in the hydraulic oil under vacuumconditions on the suction side, whereby the spring force is sodimensioned that a differential pressure of at least 0.8 bar arises witha holding pressure in the leakage compensating valve of 0.3 bar.

[0042]FIG. 4 schematically and in detail, a section through thediaphragm in its rear dead point position where it is supported on analmost gap-free surface formed by the pump body and the diaphragmcoupling disk;

[0043]FIG. 5 the design of the diaphragm as a wave diaphragm whoseintrinsic stiffness is used to generate a spring force;

[0044]FIG. 6 the design of a diaphragm with an integrated disk springfor generating the desired spring force, and

[0045]FIG. 7 schematically, a diagram of the usable working range of adiaphragm designed either as a wave diaphragm according to FIG. 5 or asa diaphragm with integrated disk spring according to FIG. 6.

[0046] As can be seen from FIG. 1, the hydraulically powered diaphragmpump shown has a diaphragm 1, which is clamped at its edge between apump body 2 and a pump cover 3 and separates a delivery chamber 4 from ahydraulic chamber 5.

[0047] The hydraulic drive of the diaphragm 1 is performed by anoscillating displacement piston 6, which is moveable back and forth inthe pump body 2 in a sleeve 7 between the hydraulic chamber 5 and areservoir chamber 8 for the hydraulic fluid.

[0048] The diaphragm 1 is designed in the embodiment shown as athree-layered sandwich diaphragm in the shape of a moulded diaphragmwith a peripheral bead 9, whose concave side faces towards the hydraulicchamber 5.

[0049] The individual layers of the diaphragm 1, not shown in greaterdetail, are mechanically coupled in their central region by means ofsuitable disks 10, 11 which are linked, particularly screwed to eachother. The disk 11 facing towards the hydraulic chamber 5 bears acentral guide rod 12 which extends axially backwards into the hydraulicchamber 5. Arranged on this guide rod 12 is a strong compression spring13 which rests at one end on a shoulder 14 of the pump body 2 and, atthe other end, on the correspondingly shoulder-shaped end of the guiderod 12. Due to the strong spring force hereby exerted, the diaphragm 1is always pretensioned in the direction of its suction stroke, i.e. itsrear dead point. The strength of the compression spring 13 is sodimensioned that a considerable compressive force is exerted on thehydraulic fluid in the hydraulic chamber 5, so that a substantialoverpressure is built up in the hydraulic chamber 5 relative to thedelivery chamber 4. In the example illustrated, this substantialoverpressure in the hydraulic chamber 5 is always at least 1 bar greaterthan the pressure in the delivery chamber 4.

[0050] In the diagram according to FIG. 2, the differential pressure onthe diaphragm over its stroke path from the front dead point FDP to therear dead point RDP is shown schematically, whereby the differentialpressure on the diaphragm is generated here purely by the previouslydescribed spring 13. As can be seen, the spring 13 also generates adifferential pressure in the rear dead point RDP of the diaphragm of atleast 1 bar, so that there is thus always a substantial overpressure inthe hydraulic chamber 5 relative to the delivery chamber 4.

[0051] In the diagram according to FIG. 3, with vacuum conditions on thesuction side, the differential pressure on the diaphragm 1 (pressure inthe hydraulic oil) is again represented. The differential pressure isgenerated by the spring force. The effective holding pressure of theleakage compensating valve 15 is also shown as the total of thedifferential pressure on the diaphragm 1 and the holding pressure of theleakage compensating valve 15 (see FIG. 1). It is always at least 1 bar.The embodiment may, for instance, be so executed that the differentialpressure on the diaphragm 1 is at least 0.8 bar and that the holdingpressure of the leakage compensating valve 15 is dimensioned to be about0.3 bar. The effective holding pressure at the rear dead point RDP ofthe diaphragm 1 is therefore at least 1.1 bar. With leakagecompensation, the diaphragm 1 is at its rear dead point earlier than thepiston 6. The pressure in the hydraulic oil then falls to 0.7 barabsolute, or to a negative pressure of 0.3 bar.

[0052]FIG. 4 shows the diaphragm 1 in its hydraulic-side position, i.e.in its rear dead point RDP. The design is so executed that the pump body2 together with the rear diaphragm coupling disk 11 form an almostgap-free surface for supporting the diaphragm 1. As a result, thediaphragm can withstand differential pressures of up to 400 bar whenstatic without suffering damage.

[0053] In the embodiment shown by FIG. 5, the diaphragm 1′ shown isformed as a wave diaphragm. Due to its construction, this has such alevel of intrinsic stiffness that this fulfils the function of thepreviously described compression spring 13 and may be used forgenerating the desired spring force on the diaphragm 1′. The dottedlines show the working range of such a wave diaphragm 1′.

[0054] In the variant embodiment according to FIG. 6, the diaphragm 1″shown has integrated disk springs 16. These may, for instance, bevulcanised into an elastomer diaphragm and also fulfil the function tothe extent that they pretension the diaphragm in the direction of itssuction stroke with a strong spring force. Here, too, the dotted linesillustrate the working range of such a diaphragm 1″.

[0055]FIG. 7 illustrates schematically the useful working range of oneof the previously described diaphragms 1′ or 1″.

[0056] With regard to the features of the invention not described ingreater detail above, reference is also expressly made to the claims andto the drawings.

1. Hydraulically driven diaphragm pump with a diaphragm clamped at itsedge between a pump body (2) and a pump cover (3), separating a deliverychamber (4) from a hydraulic chamber (5) and pretensioned in thedirection of its suction stroke by spring force, and with a hydraulicdiaphragm drive in the form of an oscillating displacement piston (6)which is displaceable in the pump body (2) between a reservoir chamber(8) for the hydraulic fluid and the hydraulic chamber (5), characterisedin that the diaphragm (1) is so strongly pretensioned by means of springforce that it exerts a substantial compressive force on the hydraulicfluid in the hydraulic chamber (5) and that therefore a substantialoverpressure is built up in the hydraulic chamber (5) against thedelivery chamber (4).
 2. Diaphragm pump according to claim 1,characterised in that the spring force is so dimensioned that thediaphragm (1) follows the piston (6) during the suction stroke even whenthere is a vacuum in the delivery chamber (4).
 3. Diaphragm pumpaccording to claim 1 or 2 characterised in that the spring force is sodimensioned that when the pump is static, the diaphragm (1) does notmove in the direction of the compression stroke due to unavoidableinternal leakage even if there is a vacuum in the delivery chamber (4).4. Diaphragm pump according to one of the previous claims, characterisedin that the spring force is so dimensioned that the pressure in thehydraulic chamber (5) is always at least 1 bar greater than the pressurein the delivery chamber (4).
 5. Diaphragm pump according to one of theprevious claims, characterised in that the spring force is sodimensioned that there is always a differential pressure of at least 1bar on the diaphragm (1).
 6. Diaphragm pump according to one of theprevious claims, characterised in that the spring force is sodimensioned that at no time point does a negative pressure prevail inthe hydraulic chamber (5) during the suction stroke until the diaphragm(1) is mechanically supported on the pump body (2).
 7. Diaphragm pumpaccording to one of the previous claims, characterised in that the totalof the differential pressure generated by the spring force on thediaphragm (1) and the holding pressure of a sprung leakage compensatingvalve (15) is always at least 1 bar.
 8. Diaphragm pump according toclaim 7, characterised in that the differential pressure on thediaphragm (1) is very large compared with the holding pressure of theleakage compensating valve (15).
 9. Diaphragm pump according to claim 7or 8, characterised in that the differential pressure on the diaphragm(1) is dimensioned to be at least 0.8 bar and the holding pressure ofthe leakage compensating valve (15) is dimensioned to be approximately0.3 bar.
 10. Diaphragm pump according to one of the previous claims,characterised in that the strong spring force pretensioning thediaphragm (1) in the direction of the suction stroke is generated by thediaphragm (1) itself, i.e. by its shape (for instance as a wavediaphragm (1′)) and/or its material.
 11. Diaphragm pump according to oneof the claims 1 to 9, characterised in that the strong spring forcepretensioning the diaphragm (1″) in the direction of the suction strokeis generated by at least one spring element incorporated into thediaphragm (1), for instance a disk spring (16).
 12. Diaphragm pumpaccording to one of the claims 1 to 9, characterised in that the strongspring force pretensioning the diaphragm (1) in the direction of thesuction stroke is generated by a compression spring (13) arranged in thehydraulic chamber (5) supported on a central guide rod (12) connected tothe diaphragm (1), on one side against the pump body (2) and on theother side against the end of the guide rod (12), the strength of saidspring being dimensioned to correspond to the effective diaphragm area.13. Diaphragm pump according to one of the previous claims,characterised in that the diaphragm (1) is designed as a mouldeddiaphragm adapted to the differential pressure applied to it. 14.Diaphragm pump according to claim 13, characterised in that the mouldeddiaphragm has a peripheral bead (9) whose concave side faces towards thehydraulic chamber (5).
 15. Diaphragm pump according to one of theprevious claims, characterised in that the diaphragm (1) is designed asa sandwich diaphragm with at least two diaphragm layers whose individuallayers are mechanically coupled and, during the suction stroke, may bewithdrawn by the spring effect of the compression spring (13) as acomplete diaphragm packet.
 16. Diaphragm pump according to one of theprevious claims, characterised in that the diaphragm (1) is supported inits rear dead point position by an almost gap-free surface formed bypart of the pump body (2) and a diaphragm coupling disk (11).